1. Field of the Invention
The present invention relates to an electrode mounting structure of a surface treatment apparatus for pre-plating or plating a surface of an object to be treated of an object, especially, a cylinder inner-peripheral surface of a cylinder of an engine.
2. Description of the Related Art
In a surface treatment apparatus for pre-plating or plating a cylinder inner-peripheral surface of a cylinder, it is necessary to periodically perform maintenance for an electrode to clean it or to renew masking thereof. Because of this reason, the electrode can be attached to or detached from an electrode holder member.
In an electrode mounting structure of a conventional surface treatment apparatus disclosed in Japanese Patent Application Laid-open No. 7-305198 (Patent Publication 1), as shown in FIG. 7, an electrode 101 and an electrode holder member 102 are formed with threaded portions 103 and 104, respectively, so as to be engaged with each other. Furthermore, Japanese Patent Application Laid-open No. 2006-2204 (Patent Publication 2) discloses a structure shown in FIG. 8 in which a bolt 105 penetrating an electrode holder member 102 is screw-engaged with a threaded portion 106 of an electrode 101, and the electrode 101 is mounted on an electrode holder member 102. In FIGS. 7 and 8, cylinders 100 are objects to be treated.
According to the electrode mounting structures described in the Patent Publications 1 and 2, however, since materials of the threaded portions (threaded portions 103 and 104 or bolt 105 and the threaded portion 106) are both composed of metals, a spark may be caused at the threaded portions, and adhesion may be caused at this threaded portion. Therefore, it becomes difficult to detach the electrode 101, and the maintenance performance of the electrode 101 becomes deteriorated.
This tendency appears seriously for a circulating plating apparatus in which circulation liquid is circulated between the electrode 101 and a cylinder inner-peripheral surface of the cylinder 100 because density of current flowing through the electrode 101 and the cylinder 100 is greater than that of an immersion-type plating apparatus.